This invention, in general, relates to electrical generators. More particularly, this invention relates to a contra rotating generator apparatus for increasing relative magnetic flux speed.
Electrical generators, in general, comprise a single rotating component called a rotor. The rotor may be either a coil wound armature or a magnetic field unit. The single rotating component of such electrical generators when designed for low rotational speeds, for example, in the range of 10 to 20 revolutions per minute, are large in physical dimensions and weight. Typically, in wind turbines, the power generated by the generator is proportional to the square of rotor blade diameter and hence there is a growing trend to build large diameter rotors, for example larger than 100 meters with each rotor blade weighing over 6 tons. The large rotor blades increase tower head weights to about 100 to 400 tons and require higher tower heights. Moreover, the fabrication of large rotor blades at wind farm sites may not be economical unless a minimum number of rotor blades are built at the same wind farm site. Furthermore, the rotor blade root-bending moment and the required wall thickness of the rotor blade increases with the square of blade length, resulting in heavier blades that further increase tower head weight. The generators with large rotor blades may therefore be difficult to transport, install, and maintain in rural or wild terrain environments.
Although in existing contra rotating wind turbines a first rotor and a second rotor rotate in opposite direction, the magnetic field between the armature and the magnetic field unit creates a cogging torque between the first rotor and the second rotor. The cogging torque causes the second rotor of the wind turbine to rotate in the same direction as the first rotor instead of the opposite direction at low wind speeds. Moreover, due to the heavy weight of the armature, an excess amount of aerodynamic torque may be required to start the rotors rotating, Furthermore, due to small air gap between the armature and the magnetic field unit of the contra rotating wind turbines, the first rotor and the second rotor may come in contact while rotating, thereby resulting in damage of the contra rotating wind turbine.
Hence, there is a need for a contra rotating generator apparatus to increase relative magnetic flux speed with reduced generator physical dimensions, weight, and cost.